Problem: Solve for $x$ : $21 = x - 5$
Solution: Add $5$ to both sides: $ \begin{eqnarray} \\ \hphantom{21 {+ 5}} &\hphantom{=}& \hphantom{x} \\ 21 &=& x - 5 \\ \\ {+5} && {+5} \\ \end{eqnarray} $ $ \begin{eqnarray} \\ 21 {+ 5} &=& x \\ \end{eqnarray} $ Simplify. $ x = 26$